Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quem é o oponente quando a pontuação era 6-4, 6-2 e a superfície era de saibro?
 ###Tabelas: CREATE TABLE round_robin_standings (round_robin_standings_id AUTO_INCREMENT PRIMARY KEY, Locale VARCHAR, Skip VARCHAR, W INT, L INT, PF INT, PA INT, Ends Won INT, Ends Lost INT, Blank Ends INT, Stolen Ends INT, Shot Pct. INT) CREATE TABLE production_and_source (production_and_source_id AUTO_INCREMENT PRIMARY KEY, Country VARCHAR, Electricity production (Kw/h, billion) INT, % Coal INT, % Natural gas INT, % Oil INT, % Hydropower INT, % Other renewable INT, % Nuclear power INT) CREATE TABLE most_starts (most_starts_id AUTO_INCREMENT PRIMARY KEY, Name VARCHAR, Period VARCHAR, Starts INT, Wins INT, Losses INT, Ties INT, Win % INT) CREATE TABLE singles:_18_5–13 (singles:_18_5–13_id AUTO_INCREMENT PRIMARY KEY, Outcome VARCHAR, Date VARCHAR, Tournament VARCHAR, Surface VARCHAR, Opponent VARCHAR, Score VARCHAR) CREATE TABLE archbishops (archbishops_id AUTO_INCREMENT PRIMARY KEY, Archbishop VARCHAR, Born VARCHAR, Ordained Priest VARCHAR, Ordained Bishop VARCHAR, Appointed Archbishop VARCHAR, Vacated throne VARCHAR, Died VARCHAR)  
SELECT Opponent FROM singles:_18_5–13 WHERE Score = 6–4, 6–2 AND Surface = clay